Droplet actuators are used to conduct a wide variety of droplet operations. A droplet actuator typically includes two substrates separated to form a droplet operations gap. The substrates include electrodes for conducting droplet operations. The gap between the substrates is typically filled with a filler fluid that is immiscible with the liquid that is to be subjected to droplet operations. Droplet operations are controlled by electrodes associated with one or both of the substrates. Because the volume of a sample of interest and/or the concentration of a target substance within a sample of interest may not be suitable for processing in a droplet actuator, there is a need for alternative approaches to preparing sample for analysis on a droplet actuator. For example, there is a need for concentrating analytes into a small volume for analysis on a droplet actuator. Further, in some droplet actuator applications there is a need for using “beads” in droplets for conducting various protocols. For protocols that make use of beads, the beads are typically used to bind to one or more target substances in a mixture of substances. The target substances may, for example, be analytes or contaminants. There is a need for alternative approaches for using beads in a droplet actuator. For example, there is a need for concentrating analytes into a small volume for analysis on a droplet actuator.